The present invention relates to fuser oil compositions, fusing of developed xerographic images and more particularly to compositions and processes which are effective in minimizing or eliminating volatile emissions from the heated fuser oil composition during thermal and or pressure fusing operations. The compositions which are particularly effective as volatile emission inhibitors or suppressants and as release agents for a variety of metal, elastomeric, or composite fuser substrates contain blends comprised of: an amino functional, a trifluoro functional, or nonfunctional organopolysiloxane; and a mercapto functional polysiloxane having at least one mercaptan group.
Various compositions have been proposed for treating fuser roll and belt substrates to impart release properties thereto. However, many of these compositions, in particular those comprised of organopolysiloxanes and various derivatives thereof, suffer from thermal instability when heated to fusing temperatures, for example about 150.degree. C. and above for short periods of time of, for example, about 0.5 seconds and longer. Thermal degradation of organopolysiloxane release agents, such as dimethylsilicone oils and related derivatives may result in the generation of volatile byproducts, for example, formaldehyde (CH.sub.2 .dbd.O), formic acid (HCO.sub.2 H), carbon dioxide (CO.sub.2), carbon monoxide (CO), hydrogen (H.sub.2), methanol (CH.sub.3 OH), ammonia (NH.sub.3), hydrogen sulfide (H.sub.2 S), trifluoropropionaldehyde (CF.sub.3 CH.sub.2 CH .dbd.O), and the like, which byproducts are potentially objectionable odor and mucousal irritants in the ambient environment of an operating xerographic machine. The byproducts may also be harmful to machine components and subsystems, such as photoreceptor belts or fuser rolls, promoting premature failure. Further, the byproducts may remain dissolved in the release agent oil and may promote continued or accelerated degradation of the silicone release agent oil composition thereby leading to undesirable changes in release agent viscosity, release properties, and perhaps negatively impacting optimal fusing performance of the fusing subsystem. The volatile emissions also have an unpleasant odor and are potentially hazardous to machine operators or passersby, particularly with prolonged exposure. Volatile emissions from fused copy or prints, that is volatiles that are dissolved in the release agent oil, may become imbibed into paper fibers, synthetic receiver sheet materials, or fixed toner images, and may outgas over time and may further pose an objectionable odor or irritation problem which may lead to reduced customer acceptance and satisfaction.
Other sources of volatile emission components include residuals from preparative reactions or purification processes residing in the oil itself, such as solvents, monomers, initiators, impurities, and the like; and degradation products arising from various oil performance additives. Commercial manufacturers and suppliers of silicone release agent oil products routinely employ additional processing steps to purposely "devolatilize" their products in recognition of volatile emissions being a problem for corrosion or contamination of mechanical and electrical machine components.
Antioxidant additives for silicone fluids are known. J. M. Nielsen in "Stabilization of Polymers and Stabilizer Processes", Advances in Chemistry Series, Vol. 85, American Chemical Society, Washington D.C., 1968, provides an early account of antioxidant additives for silicone fluids including, for example, redox metal complexes and soaps which are however disadvantaged by producing haze, gels or sludge on storage and or during use, and interfering with copy quality and color print fidelity.
T. S. Heu in Journal of the Korean Rubber Society, Vol. 18, No. 1, pages 21 to 29 (1983) describes the stability and degradation prevention of silicone oils and rubbers. Silicone compound stability is categorized into oxidation stability and thermal stability. Oxidation stability refers to resistance of the silicone compound to react with oxygen which reactions lead to intermolecular cross-linking and increased viscosity for silicone liquids and hardening for silicone rubbers. Thermal stability refers to the resistance of the silicone compound to undergo intramolecular cleavage of siloxane bonds (Si--O--Si) by heat which reactions produce lower molecular weight products and leads to reduced viscosity for silicone oils and softening of silicone rubbers. Resistance to both pathways of degradation is called thermal oxidation stability. Homologous hydrocarbon structural derivatives of dimethyl polysiloxanes such as ethyl, propyl, butyl, and the like, generally possess lower thermal stability than the dimethyl compound. Certain structural derivatives of polysiloxanes have enhanced thermal stability, for example, phenyl methyl siloxane, but these derivatives are disadvantaged by their higher cost and thermal degradation liberates benzene. Thermal stability for silicone oils having the same repeat unit is generally higher for the oil with the greater molecular weight.
Additives made from, for example, salts of organometallic acids are commonly used to improve the thermal oxidation stability of silicone oils. However, these salts chemically react with the silicone oil in a multitude of ways as part of the stabilization mechanism and therefore unpredictably lead to oils having significantly altered physical, for example, viscosity and performance, for example, release properties.
The following United States Patents are of interest:
U.S. Pat. No. 4,029,827, to Imperial et al, issued Jun. 14, 1977, discloses polyorganosiloxanes having functional mercapto groups, are applied to a heated fuser member in an electrostatic reproducing apparatus to form thereon a thermally stable, renewable, self-cleaning layer having superior toner release properties for electroscopic thermoplastic resin toners.
U.S. Pat. No. 4,251,277, to Martin, issued Feb. 17, 1981, discloses compositions containing organopolysiloxanes and thiofunctional polysiloxanes having at least one mercaptan group which are effective as corrosion inhibitors and as release agents for metal substrates.
U.S. Pat. No. 4,515,884 to Field et al, issued May 7, 1985, discloses a method of fusing by providing a silicone elastomer fusing surface, heating the fuser member to fuse toner particles to the receiver substrate, applying directly to the silicone elastomer fusing surface in non-emulsified form an unblended polydimethylsiloxane having a viscosity of about 7,000 to about 20,000 centistokes, and contacting the toner image on the substrate with the toner release agent which includes an unblended polydimethyl siloxane
In xerographic applications, it is desirable to use release agent oils which are: cost effective; clear; colorless; odorless or nearly so at room temperature and at fuser operating temperatures; free of additives such as acids, bases, peroxides, heavy metals, and the like, that can interfere with the fusing and sheet release performance of the fusing system and associated hardware; and free of or produce minimal volatile emission component(s) over the service life of the release agent oil.
Thus, there remains a need for improved oxidative or thermal stability of organopolysiloxane release agent fluids to minimize or eliminate the emission of volatile compounds, such as formaldehyde, at fuser operating temperatures. The need is preferably achieved without the use of an external additive package or without compromising or diminishing the release properties of the oil. Failure to satisfy the aforementioned need suggests that machine users will continue to be exposed to potentially hazardous or unpleasant odors due to degradative generation or evaporation of dissolved volatile compounds, such as formaldehyde, from release agent oil compositions comprised of polydiakylsilicone and derivative silicone oils at fuser roll operating temperatures.